1. Technical Field
The present invention relates to an ink tank with an ink absorbing member absorptively retaining ink, and more particularly to an ink tank with a detected portion capable of exactly detecting when ink in the ink tank has been depleted, including the amount of ink used or remaining in the ink tank, and an ink jet printer using the ink tank as an ink supplying source.
2. Related Art
An ink tank of a foam type is known for the ink tank of an ink jet printer. The foam type ink tank is composed of a foam containing part containing a foam absorptively retaining ink, an ink outlet communicating with the foam containing part, and an air communication port through which the foam containing part is opened to the air. When ink is sucked through the ink outlet in response to an ejection pressure of the ink jet head, an-amount of air corresponding to an amount of sucked ink flows from the air communication port to the foam containing part.
In the case of the foam type ink tank, detection as to whether ink is present is carried out based on a count result, viz., in a manner that an amount of used ink is counted in accordance with the number of ink dots ejected from the ink jet head, and an amount of ink sucked by the ink pump which sucks ink from the ink jet head, or the like.
Generally, a contents state of the ink tank in which little ink is left in the ink tank is called a “real end”. A contents state of the ink tank in which an amount of ink left in the ink tank is smaller than a predetermined amount of ink is called a “near end”. In the present specification, the term “ink end” involves both the terms “real end” and “near end” unless otherwise stated or indicated.
The ink end detecting method, which counts the amount of used ink and detects the ink end based on the count result, has the following problems. First, some variations are present in the amount of ejected ink in the ink jet head and the amount of ink sucked by the ink pump. An amount of used ink that is counted on the basis of those ink amounts may greatly deviate from the amount of ink actually used. Therefore, the necessity is that a large margin must be set up to definitively determine the ink end state. The result is that at a time point where the ink end is detected, a great amount of ink is often still left, thereby resulting in the waste of ink.
A possible way to solve the problem is that the ink end is directly detected by using an optical detecting system which utilizes the reflecting surface of a prism which resumes its original reflecting surface function when the ink is used up. The detecting system utilizing the prism reflecting surface is disclosed in, for example, JP-A-10-323993 and U.S. Pat. No. 5,616,929.
In the case of the foam type ink tank, the ink is absorptively retained in the foam. Therefore, it is impossible to directly apply the detecting system disclosed in the patent publication to the ink tank. A possible solution to this is that a sub ink chamber of a small capacity, which can store ink, is located between a main ink chamber (foam containing part containing a foam), and the ink outlet. The reflecting surface of the prism is disposed in the sub ink chamber. In a state that a certain amount of ink in the main ink chamber is consumed, air flows into the sub ink chamber.
By so doing, every time ink is supplied through the ink outlet, ink flows from the main ink chamber to the sub ink chamber. As the amount of ink in the main ink chamber becomes small, air bubbles enter the main ink chamber. Over the course of time, the ink in the main ink chamber is used up, and the only ink remaining in the ink tank is the ink stored in the sub ink chamber.
When the amount of ink left in the sub ink chamber is reduced to be small, the reverse surface of the reflecting surface of the prism, which serves as an ink interface, becomes exposed above the ink liquid surface, and a reflecting state of the reflecting surface changes. More particularly, the reverse surface of the prism, which does not function as the reflecting surface when it is covered with ink, gradually resumes its original function of the reflecting surface as the ink liquid level lowers. Accordingly, a state in which the amount of residual ink is smaller than a predetermined amount of ink can be detected based on the amount of light reflected by the reflecting surface. Therefore, if the volume of the sub ink chamber is sufficiently small, the ink end can be detected at a time point where the amount of residual ink is substantially zero.
When air bubbles having entered the sub ink chamber stick to the reverse surface of the prism reflecting surface or stray in the vicinity of the reverse surface, the prism reflecting surface remains covered with ink retained among the air bubbles even if the ink liquid surface lowers to a level below the prism reflecting surface. As a result, a reflecting state of the prism reflecting surface remains unchanged even if the ink liquid surface lowers. As such, a disadvantageous situation in which it is impossible to detect the ink end possibly occurs.